The present invention relates generally to vapor recovery systems associated with both automobiles and fuel dispensers. More particularly, the invention relates to a fill neck vapor block for ORVR-equipped vehicles and its use as a means to detect the presence of an ORVR vehicle.
For the past several years, the environmental regulations have imposed limits on the amount of fuel vapor released into the atmosphere during the refueling of a motor vehicle. During a non-vapor-recovery fueling operation, incoming fuel displaces fuel vapor from the head space of an automobile fuel tank, forcing the vapors out through the filler pipe into the atmosphere. The air pollution resulting from this situation is undesirable. Currently, many fuel dispensing pumps at service stations are equipped with vapor recovery systems that collect fuel vapor in the fuel tank filler pipe during the fueling operation and transfer the vapor to a fuel storage tank. Many of these systems include a vapor pump to positively move vapor from the filler pipe to the service station's fuel tanks and are commonly referred to as vacuum assist systems.
Recently, onboard, or vehicle-carried, fuel vapor recovery and storage systems (commonly referred to as onboard recovery vapor recovery, or ORVR) have been developed, in which the head space in the vehicle fuel tank is vented through an activated carbon filled canister so that the vapor is adsorbed by the activated carbon. Subsequently, the fuel vapor is withdrawn from the canister into the engine intake manifold for mixture and combustion with the normal fuel and air mixture.
In typical ORVR systems, a canister outlet is connected to the intake manifold of the vehicle engine through a normally closed purge valve. The canister is intermittently subjected to the intake manifold vacuum with the opening and closing of the purge valve between the canister and intake manifold. A computer which monitors various vehicle operating conditions controls the opening and closing of the purge valve to assure that the fuel mixture established by the fuel injection system is not overly enriched by the addition of fuel vapor from the canister to the mixture. An example of an ORVR system is described in U.S. Pat. No. 4,887,578 to Woodcock et al.
Fuel dispensing systems having vacuum assisted vapor recovery capability which are unable to detect ORVR systems ingest excessive air into the underground storage tank and cause excessive pressure build-up in the underground storage tank due to the delivery of air rather than fuel vapor. The air causes further liquid fuel vaporization leading to "vapor growth." Recognizing an ORVR system and adjusting the operation of the fuel dispenser's vapor recovery system accordingly eliminates the redundancy and problems associated with operating two vapor recovery systems for one fueling operation. The problem of incompatibility of assisted vapor recovery and ORVR was discussed in "Estimated Hydrocarbon Emissions of Phase II and Onboard Vapor Recovery Systems" dated Apr. 12, 1994, amended May 24, 1994, by the California Air Resources Board. That paper suggests the use of a "smart" interface on a nozzle to detect an ORVR vehicle and prevent the return of vapors through the nozzle when an ORVR vehicle is being filled. However, such a nozzle may prove expensive and may require excessive maintenance.
Adjusting the operation of the fuel dispenser's vacuum assist vapor recovery system will mitigate fugitive emissions by reducing underground tank pressure. Reducing underground tank pressure minimizes the "breathing" associated with pressure differentials between the underground tank and ambient pressure levels. If the vacuum created by the fuel dispenser's vapor recovery system is not reduced or shut off, the underground tank pressure will increase with the result that hydrocarbons will be released through piping leaks or a pressure vacuum valve or breathing cap associated with the underground tank.
Thus, there remains a need for a vapor recovery system modification having the ability to modify vacuum assist system operation when an ORVR system is present on the vehicle being fueled to reduce breathing losses.